Edfm-Based Reservoir Simulation for Water Breakthrough Evaluation in Naturally Fractured Reservoirs

Abstract Water breakthrough is a common challenge in naturally fractured reservoirs in many places. Though reservoir simulation plays a key role for the engineers to understand and evaluate this situation, conventional approaches, such as dual porosity, may lead to excessive computation and unrealistic results. In our work, we used an embedded discrete fracture model (EDFM) to solve the problem. The workflow that we created, involving fracture evaluation, modelling, and simulation, better described the process of water breakthrough in fractured reservoirs, and provided strong support for development planning and decision making in similar reservoirs. Our work took place in Block-A from a buried-hill structure in offshore China. The oil reservoir from this block was highly fractured and the pressure support from the bottom water was relatively weak. There were seven producers and two injectors deployed in the early phase of the development, which showed high initial production but surprisingly rapid water break-though. A conventional dual-porosity model was used to simulate the situation, yet the performance was not satisfactory. An EDFM-based solution was proposed to solve the problem, as EDFM had a unique advantage to handle complex fracture networks efficiently in the form of additional discrete entities explicitly modelled with their geometry, orientation, and properties that interact with the surrounding porous matrix grids. In our work, the natural fracture key parameters, including the aperture, length, and average permeability, were derived from a formation image log and well testing result. Those properties were modelled in the reservoir grid together with EDFM definitions, so that the simulator engine would not only include the grid-to-grid interaction, but also grid-to-fracture and fracture-to-fracture dynamics via the non-neighboring-connection (NNC) settings. The simulator performance with EDFM is robust and highly efficient, and it clearly showed that the natural fractures led the early breakthrough through the high conductivity channels. EDFM provides a better-performing, more-realistic reservoir simulation in naturally fractured reservoirs. Comparing with the conventional approach, EDFM improves the simulation efficiency by about 30% in our work and shows better details of the reservoir dynamics in its matrix and the fractures, revealing the dominant impact of the fractures on the water breakthrough.